Planetary wheel end assemblies include a planetary gear assembly that receives driving input from an axle shaft. A typical planetary gear assembly includes a sun gear that is fixed for rotation with the axle shaft, a plurality of planet gears, a ring gear, and a planetary spider that supports the planet gears. In one known configuration, the ring gear is fixed to a non-rotating component, such as a housing for example, and the planetary spider provides driving output for a wheel component.
Typically, the sun gear comprises a cylindrical gear body having an outer peripheral surface with a plurality of sun gear teeth and an inner peripheral surface that includes a set of sun gear splines. A radial wall thickness is defined in a radial direction extending between a root area at roots of the gear teeth and a spline base area at locations between adjacent sun gear splines. The axle shaft has a set of mating axle shaft splines that cooperate with the sun gear splines such that the axle shaft and sun gear rotate together. As input torque into the wheel end increases, a larger diameter axle shaft is often required. Due to high hoop stresses caused by the axle shaft splines in combination with a bending moment on the gear body generated by gear teeth bending, the remaining radial wall thickness for a traditional sun gear becomes insufficient.
Solutions have been proposed to address this condition but these solutions have been proven to be expensive and require large space to package. For example, sun gear size has been increased in a radial and axial direction but this is disadvantages from a weight and cost perspective. Further, when the sun gear is enlarged in this manner, the sun gear spline can no longer be inexpensively broached. Thus, there is a need to provide a sun gear configuration that minimizes stresses such that a sun gear spline can still be broached.